The ability to regenerate structures and biological function would be of considerable value to a large number of patients. For many years experiments have focused on identifying what types of structures, in what organisms, undergo regeneration. More recently, studies have begun to identify signal transduction pathways that might be involved in regeneration. Among these pathways are those stimulated by the 19 members of the Wnt family of secreted ligands. Wnt signaling components are expressed during regeneration in multiple species but whether Wnt signaling is occurring and whether it is important for regeneration is unknown. Our specific aims seek to resolve the major outstanding questions regarding Wnts and regeneration. Aim 1: Is Wnt signaling activated during regeneration and if so, in which cells? Aim 2: Is Wnt signaling necessary for regeneration to occur, as determined by loss of function experiments? Aim 3: Can gain of function of Wnt signaling enhance regeneration? Finally, Aim 4 will seek to identify Wnt-responsive genes during regeneration and to study their roles in regeneration. By studying regeneration in Xenopus tadpoles, adult zebrafish, and the injured mouse spinal cord we have preliminary data supporting the first three aims, thereby establishing that Wnt signaling is indeed involved and functional in regeneration. The benefit of simultaneously employing frogs, fish, and mice in our project is that we can determine whether the roles of Wnt signaling in regeneration are conserved between species. Thus the general significance of the proposal is that we have a focused set of experiments that will reveal whether or not Wnt signaling is necessary and sufficient for stimulating regeneration in vertebrates. The immediate relevance to human medicine is that we directly test whether Wnt signaling improves the ability of neural stem cells to promote regeneration in a mouse model of spinal cord injury. This research therefore builds upon experiments in various model organisms to contribute to the development of therapies.